1. Field of the Invention
This invention relates to a vibration isolation apparatus and methods. Particularly, this invention relates to methods and apparatus for an active vibration isolation system (AVIS) that use a combination of pneumatic control system and electronic control system to support a mass and isolate the mass from external disturbances, such as vibration. The AVIS may be used in a photolithography process.
2. Description of the Related Art
Photolithography is used for manufacturing integrated circuits. Light is transmitted through non-opaque portions of a pattern on a reticle, or photomask, through a projection exposure apparatus, and onto a wafer of specially-coated silicon or other semiconductor material. The uncovered portions of the coating that are exposed to light harden. The unhardened coating is then removed by an acid bath. Thus, the layer of uncovered silicon is altered to produce one layer of the integrated circuit. Conventional systems use visible and ultraviolet light for this process. Recently, however, visible and ultraviolet light have been replaced with electron, X-ray, and laser beams, which permit smaller feature sizes in the patterns.
As the miniaturization of a circuit pattern progresses, the focus depth of the projection exposure apparatus becomes very small. As a result, a primary consideration for an overall design of the photolithography system includes building components of the system that achieve precision by maintaining small tolerances. Any vibration, distortion, or misalignment caused by external or environmental disturbances must be kept at minimum. These external disturbances affecting an individual part collectively alter the focusing properties of the photolithography system.
Environmental effects may come from, among other things, heat generated by an electric motor that drives the wafer carrying stage device. The heat generated from the motor spreads to the surrounding environment changing index of refraction of the surrounding gas. In addition, heat also affects the neighboring components causing the components of the photolithography system to expand according to their coefficients of thermal expansion.
Environmental effects may also come from vibrations from moving parts, the ground, or other aspects. Therefore, in a sensitive system where alignment accuracy is essential, such as a lithography system to manufacture semiconductor wafers, there is a need for an isolation system to substantially reduce vibration.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and consistent with the principles of the invention, as embodied and broadly described herein, a first aspect of the invention is a method for operating a vibration isolation system having a pneumatic contOorl system and an electronic control system. The method comprises the step of generating a pneumatic force in the pneumatic control system to support a mass. The pneumatic force is produced by a pressure level in a compliance chamber. The pressure level is being controlled in response to a pressure error signal. The method also comprises the steps of delivering the pressure error signal to the electric control system, and monitoring a motion error signal of the mass in the electronic control system. The motion error signal is being used to generate an electronic force to isolate the mass from vibration. The electronic force is being determined based on a combination of the pressure error signal and the motion error signal.
A second aspect of the present invention is a method for operating a vibration isolation system having a pneumatic control system and an electronic control system. The method comprises the step of monitoring a motion error signal of a mass in the electronic control system. The motion error signal is being used to generate an electronic error signal. The method also comprises the steps of delivering the electronic error signal to the pneumatic control system, and generating a pneumatic force in the pneumatic control system to support the mass. The pneumatic force is being determined based on a combination of the electronic error signal and a pressure level in a compliance chamber. The pressure level is being controlled in response to a pressure error signal. The method further comprises the steps of delivering the pressure error signal to the electric control system, and generating an electronic force in the electronic control system to isolate the mass from vibration. The electronic force is being determined based on the pressure error signal.
A third aspect of the present invention is a method for operating a vibration isolation system having a pneumatic control system and an electronic control system. the method comprises the steps of generating a pressure error signal in the pneumatic control system based on a pressure signal of a compliance chamber and a reference pressure signal, and controlling the pressure level in the compliance chamber in response to the pressure error signal, the compliance chamber generating a pneumatic force in proportion to the controlled pressure level to pneumatically support a mass. The method also comprises the steps of delivering the pressure error signal to the electronic control system, comparing a motion signal of the mass in the electronic control system with a reference motion signal to generate a motion error signal, and combining the motion error signal and the pressure error signal. The method further comprises the step of determining an electronic force to isolate the mass from vibration based on the combined motion and pressure error signals.
A fourth aspect of the present invention is a method for operating a vibration isolation system having a pneumatic control system and an electronic control system. The method comprises the steps of comparing an actual motion signal of a mass in the electronic control system with a reference motion signal to generate a motion error signal, determining an electronic error signal based on the motion error signal, and delivering the electronic error signal to the pneumatic control system. The method also comprises the steps of comparing a pressure signal of a compliance chamber in the pneumatic control system with a reference pressure signal and combining the electronic error signal thereto to generate a pressure error signal, and controlling the pressure level in the compliance chamber in response to the pressure error signal. The compliance chamber generates a pneumatic force proportionate to the controlled pressure level to pneumatically support the mass. The method further comprises the steps of delivering the pressure error signal to the electronic control system, and determining an electronic force in the electronic control system based on the pressure error signal to isolate the mass from vibration.
A fifth aspect of the present invention is a vibration isolation system, comprising a pneumatic control system having a compliance chamber to generate a pneumatic force that supports a mass based on a pressure error signal, and an electronic control system having a motion sensor to generate a motion error signal of the mass. The vibration isolation system also comprises a force generator connected with the pneumatic control system and the electronic control system. The force generator generates an electronic force based on the results of a combination of the pressure error signal and the motion error signal to isolate the mass from vibration.
A sixth aspect of the present invention is a vibration isolation system having a pneumatic control system and an electronic control system. The vibration isolation system comprises a motion sensor, a compliance chamber, a pressure sensor, a pneumatic force generator, and an electronic force generator. The motion sensor generates a motion error signal of a mass in the electronic control system. The motion error signal is being used to generate an electronic error signal. The compliance chamber and the pressure sensor are provided in the pneumatic control system. The pressure sensor controls a pressure level in the compliance chamber to generate a pressure error signal. The pneumatic force generator is connected to the compliance chamber and electronic control system. The pneumatic force generator generates a pneumatic force that supports the mass based on the results of a combination of the electronic error signal and the pressure level in the compliance chamber. The electronic force generator is connected to the pneumatic control system. The electronic force generator generates an electronic force that isolates the mass from vibration based on the pressure error signal.
A seventh aspect of the present invention is a vibration isolation system having a pneumatic control system and an electronic control system. The vibration isolation system comprises a pressure sensor and a first controller. The pressure sensor generates a pressure error signal based on a pressure information of a compliance chamber and a reference pressure information. The first controller is connected to the pressure sensor for controlling a pressure level in the compliance chamber in response to the pressure error signal. The vibration isolation system also comprises a pneumatic force generator, a second controller, and an electronic force generator. The pneumatic force generator is connected to the first controller for generating a pneumatic force determined based on a controlled pressure level to pneumatically support a mass. The second controller is connected to the first controller for comparing a motion information of the mass with a reference motion signal to generate a motion error signal, and for generating an electronic force signal based on the motion error signal and the pressure error signal. The electronic force generator is connected to the second controller for generating an electronic force to isolate the mass from vibration based on the motion error signal and the pressure error signal.
An eighth aspect of the present invention is a vibration isolation system having a pneumatic control system and an electronic control system, comprising four controllers. The first controller compares an actual motion signal of a mass in the electronic control system with a reference motion signal to generate a motion error signal and to determine an electronic error signal based on the motion error signal. The second controller compares a pressure signal of a compliance chamber in the pneumatic control system with a reference pressure signal, and to combine the electronic error signal thereto to generate a pressure error signal. The third controller controls the pressure level in the compliance chamber in response to the pressure error signal. The compliance chamber generates a pneumatic force proportionate to the controlled pressure level to pneumatically support the mass. The fourth controller determines an electronic force in the electronic control system based on the pressure error signal to isolate the mass from vibration.
A further aspect of the present invention is a vibration isolation system using the methods as summarized in the above aspects of the invention. Yet, a further aspect of the present invention is a lithography system comprising the vibration isolation system and an object on which an image has been formed by the lithography system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims.